Although its use is not limited thereto, the present invention has particular application to mechanical grape harvesters wherein a main frame is supported by wheeled columns at the four corners thereof, the harvester being adapted to straddle and move along a row of grape vines while a picking apparatus mounted on the frame agitates the vines, causing the fruit to be dislodged to fall into catchers and conveyors carried by the frame and disposed beneath the vines.
In order to provide optimal harvesting, such a harvester should have a number of attributes. First, it should have the capability of raising and lowering the frame relative to the ground so that the picking apparatus, catchers and conveyors carried by the frame can be properly positioned relative to the height of the vines. Secondly, it should have the capability of maintaining the frame level, from side-to-side thereof, as the harvester travels across the slope of the hill with its downhill wheels lower than the uphill wheels. In such case, it is desirable that the frame be maintained level on sloping terrain with the elevation of the frame above the uphill wheels being held constant. Since either side of the harvester can be the "uphill" side, depending upon the direction of travel across the slope, the harvester must be capable of maintaining the frame level relative to the uphill side regardless of which side is uphill. Further, it is desirable that the harvester be capable of maintaining the frame level with respect to the longitudinal centerline of the machine, when so desired.
Also, a harvester should have the capability of operating on rough ground, with the many ditches and bumps found in vineyards, with all four wheels maintained in firm ground engagement. Otherwise, if one wheel comes to a ditch and the frame is then supported only by the other three wheels, the one wheel with simply spin in the air and traction thereat will be lost. The same, of course, will occur if one wheel rides up on a bump so that the frame is again supported by only three wheels.
In my prior U.S. Pat. No. 3,909,022, issued Sept. 30, 1975, I have disclosed a cable suspension system for a harvesting machine which is capable of raising and lowering the frame relative to the wheeled columns, maintaining the frame level about its uphill side or the longitudinal centerline thereof, and capable of maintaining all four of the wheel columns on engagement with the ground in spite of unevenness of the ground.
In practice, however, the cable suspension system has evidenced two disadvantages--wear and breakage of the cables and inability of the front columns of the harvester to accomodate to an abrupt change in side slope.
These disadvantages have been overcome in the present invention by use of a hydraulic suspension having a hydraulic ram at each of the wheeled columns and a control system therefor which provides all of the desired capabilities enumerated above.